The present invention relates to an assembly including a structural member or frame that supports a load, and more particularly, to electro-hydraulic control systems for mineral mining installations.
Underground mining machines are usually powered using electricity and electric motors. In order to house the controls for these motors, a controller case is employed. A controller case for use in a gaseous mine environment must be certified explosion proof and this is accomplished by constructing it as a robust box made from steel with a finely machined cover which is screwed onto a machined flange.
This fit of the cover to the flange is known as the flame path. It must adhere to strict specifications in order to be effective at preventing an explosion from occurring when there are flammable gases outside the controller. These covers usually employ a number of closely spaced cap screws securing them to the controller case.
When mining machines are used in low seams, the size of the controller must be minimized. In some cases it is advantageous to make the controller case a structural member of the machine frame in order to maximize the internal volume of the controller while minimizing the size of the machine. In other words, the controller box is not installed in a space in the frame; it becomes the frame. Another common characteristic of a mining controller is the use of a cover that is substantially one entire side of the case. This is done to allow generous access to install the components in the case initially as well as troubleshooting after the machine has been put into production.
When the controller is a structural member of the machine, the stresses exerted on the controller case can cause the screws that mount the covers to loosen or fracture, but these controllers are required to be explosion proof in order to prevent an internal electrical spark from igniting a gaseous mine atmosphere.